This invention relates to reproduction apparatus and more particularly to cleaning apparatus for removing residual toner and debris from a charge retentive surface including a secondary cleaning system for release and removal of agglomerates from the surface that are not cleaned therefrom at the primary cleaner.
In electrophotographic applications such as xerography, a charge retentive surface is electrostatically charged, and exposed to a light pattern of an original image to be reproduced to selectively discharge the surface in accordance therewith. The resulting pattern of charged and discharged areas on that surface form an electrostatic charge pattern (an electrostatic latent image) conforming to the original image. The latent image is developed by contacting it with a finely divided electrostatically attractable powder referred to as "toner". Toner is held on the image areas by the electrostatic charge on the surface. Thus, a toner image is produced in conformity with a light image of the original being reproduced. The toner image may then be transferred to a substrate (e.g., paper), and the image affixed thereto to form a permanent record of the image to be reproduced. Subsequent to development, excess toner left on the charge retentive surface is cleaned from the surface. The process is well known, and useful for light lens copying from an original, and printing applications from electronically generated or stored originals, where a charged surface may be imagewise discharged in a variety of ways. Ion projection devices where a charge is imagewise deposited on a charge retentive substrate operate similarly.
Although a preponderance of the toner forming the image is transferred to the paper during transfer, some toner invariably remains on the charge retentive surface, it being held thereto by relatively high electrostatic and/or mechanical forces. Additionally, paper fibers, Kaolin and other debris have a tendency to be attracted to the charge retentive surface. It is essential for optimum operation that the toner remaining on the surface be cleaned thoroughly therefrom.
A commercially successful mode of cleaning employed in automatic xerographic devices utilizes a brush with soft conductive fiber bristles which have suitable triboelectric characteristics. While the bristles are soft they are sufficiently firm to remove residual toner particles from the charge retentive surface. A voltage is applied to the fibers to enhance removal of toner from the charge retentive surface.
Not all toner and debris is removed from the surface by the brush cleaner. For reasons that are unclear, toner particles agglomerate with themselves and with certain types of debris to form a spot-wise deposition that can eventually strongly adhere to the charge retentive surface. These spots range from 50 .mu.m to greater than 400 .mu.m in diameter and 5-25 .mu.m in thickness, but typically are about 200 .mu.m in diameter and 5-15 .mu.m in thickness. The agglomerates range in material compositions from nothing but toner to a broad assortment of plastics and debris from paper. The spots cause a copy quality defect showing up as a black spot on a background area of the copy which is the same size as the spot on the photoreceptor. The spot on the copy varies slightly with the exact machine operating conditions, but cannot be deleted by control of the machine process characteristics.
While attempts were made to eliminate the agglomerate spotting by controlling of extraneous debris within the device, this solution has been found difficult if not impossible to implement. Additionally, there was no way to eliminate the formation of agglomerates that the toner formed itself. However, in studying the formation of these spots, it was noted that the spots appeared instantaneously on the charge retentive surface, i.e., the spots were not the result of a continuing nucleation process. It was subsequently noted that newly deposited spots were more weakly adhered to the surface than older spots.
The combination in a cleaning system of a brush cleaner with a cleaning blade in residual toner removing, sealing engagement is known. U.S. Pat. No. 4,364,660 to Oda shows a fur brush in combination with a soft rubber cleaning blade, where the cleaning blade functions as the primary means for toner release from the photoreceptor, and the brush operates to remove toner accumulating at the blade to the toner collection system. U.S. Pat. No. 3,947,108 to Thettu et al, shows a brush and blade combination with the brush acts as a scrubber member for the release of accumulating toner film while the blade is the primary cleaner. In a two cycle system, where the photoreceptor rotates twice for every copying operation, U.S. Pat. No. 3,918,808 to Narita shows the use of a cleaning blade as a primary cleaner, in typical cleaning engagement adjacent a magnetic brush used for both development and cleaning. U.S. Pat. No. 4,279,501 to Kojima et al. shows a cleaning system with a cleaning roller and cleaning blade. U.S. Pat. Nos. 4,561,766 to Fox and 4,026,648 to Takahashi show various blade cleaner systems. U.S. Pat. Nos. 4,373,800 to Kamiyama et al., and 4,089,683 to Knieser show liquid developer cleaning arrangements, including respectively, a blade and squeegee roller, and a blade and foam belt. U.S. Pat. No. 4,185,399 to Gladish and U.S. Pat. No. 4,741,643 to Smith et al. each show air stream devices for cleaning liquids from a surface. IBM Technical Disclosure Bulletin, Vol. 19, No. 8, p. 3215, (January, 1977) by K. Sanders, notes the use of an air stream for the removal of toner from a cleaning brush used to clean an electrophotographic drum. These references are all incorporated by reference herein.
Upon insertion of a new blade into an electrophotographic device, high frictional forces are noted during a break in period, until the blade is properly lubricated. A fixed blade holder is prone to tuck under during break in, or startup, because of the dynamic friction forces create a bending moment which increased the normal force on the blade further. A free floating blade supporting holder tends to allow the blade to creep in the operation.